Xenorhina thiekeorum, Günther & Richards, 2021

Guenther, Rainer & Richards, Stephen, 2021, Description of six new species of Xenorhina Peters, 1863 from southern Papua New Guinea (Amphibia, Anura, Microhylidae), Zoosystematics and Evolution 97 (2), pp. 355-382 : 355

Xenorhina thiekeorum sp. nov.

Holotype.

SAMA R71651 (SJR 209047), adult male, from Ok Menga near Tabubil, Western Province, Papua New Guinea (5.3205°S, 141.3049°E; 620 m a.s.l.), collected by S.J. Richards, M. Cunningham and A. Dennis on 14-11-1994.

Paratypes.

ZMB 91131 (SJR 209051), PNGNM (SJR209052), SAMA R71652 (SJR209053), same details as for holotype.

Diagnosis.

This species of Xenorhina is characterised by the unique combination of: moderately small size (males 20.7-23.5 mm SUL); vomeropalatines each with one moderately developed triangular vomerine spike; legs moderately short (TL/SUL 0.40-0.44); all fingers and first toe without and toes 2-5 with, expanded terminal discs; tips of all fingers and toes with circum-marginal grooves that extend, at least partially, along most digits; head short (HL/SUL 0.26-0.28), eye-naris distance much greater than internarial distance (END/IND 1.36-1.54); tympanum approximately 2/3 size of eye (TyD/ED 0.63-0.69). Dorsal surfaces in life reddish-brown, covered extensively with small, white-tipped tubercles, lower flanks with larger off-white spots; back with faint yellowish mid-dorsal line. Advertisement calls uttered in series containing less than 10 short, extremely soft “piping” calls of 133-162 ms duration, produced at a rate of 2.5-3.0 calls/s.

Description of the holotype.

Measurements are summarised in Table 4 , a dorsolateral view in life is shown in Fig. 10a and ventral surfaces in life in Fig. 10b . Head broader than long (HL/HW 0.81); snout short (HL/SUL 0.27), strongly acuminate from above and below, protruding in profile; tongue long, broad, only its lateral and posterior edges free; prepharyngeal ridge with eight small denticles; vomerine spikes triangular and of moderate size; loreal region oblique, no canthus rostralis; nostrils near tip of snout, directed dorsolaterally, visible from above, but not from below; eye-naris distance significantly greater than internarial distance (END/IND 1.46); borders of tympanum poorly defined in life and preservative, its diameter 2/3 that of eye (TyD/ED 0.67); supratympanic fold not reaching posterior edge of eye or insertion of fore-leg; shank short (TL/SUL 0.40); fingers moderately short, not webbed; all fingers and first toe without and toes 2-5 with, expanded terminal discs; circum-marginal grooves on tips of all fingers and toes, extending at least partly along most digits; relative lengths of fingers 3 > 4 = 2 = 1 (Fig. 10c ); toes not webbed, relative lengths 4 > 3 > 5 > 2 > 1 (Fig. 10d ); plantar and palmar tubercles as well as subarticular tubercles poorly defined. Dorsal surfaces with scattered low tubercles and a slightly raised yellowish mid-dorsal ridge, ventral surfaces smooth.

In life, dorsal surfaces brown beige (RAL 1011) with irregularly shaped, indistinct lighter markings in lumbar region and narrow, pale mid-dorsal line; dorsum with numerous small, white-tipped tubercles; lower flanks and anterior and posterior of tympana with whitish spots; dorsal surfaces of limbs and dorsal edge of tympana with few dark brown spots and/or streaks; iris blackish with scarcely visible golden veins and solid golden inner margin. Colour of ventral surfaces in life was not documented.

In preservative, ground colour of dorsal surfaces reddish-brown; dorsolateral surfaces with conspicuous blackish-brown spots, mostly associated with white-tipped tubercles; extremities and anterior back with lighter brown flecks than those on dorsolateral surfaces; solid reddish-brown areas of back merge on lower flanks into ivory-white ground colour of ventral surfaces, which are covered by a dense orange-brown reticulum.

Morphological variation.

Measurements of the type series are summarised in Table 4 . Ground colour of dorsal surfaces in preservative is the same in all types (including holotype), except SAMA R71652 which is slightly paler; number and intensity of brown dorsal and lateral spots varies slightly. Ventral surfaces and rear of thighs in all frogs show a more or less dense orange brown reticulum on ivory-white ground.

Distribution and ecological notes.

Xenorhina thiekeorum sp. nov. is known only from the type locality adjacent to the Ok Menga ( “Ok” = River in the local Min language), at an altitude of 620 m a.s.l. in the foothills of the Hindenburg Range, Ok Tedi headwaters in Western Province, Papua New Guinea (Fig. 16 ). The frogs were calling from 1-3 cm beneath the soil surface at the base of ginger plants after rain at night. Unlike many Xenorhina species, the distribution of calling males was “clumped”; all four frogs were detected by their calls within an area of approximately 4 m2 of wet hill forest, while none was heard calling in apparently suitable adjacent forest.

Vocalisation.

Three call series from the holotype ( SAMA R71651) recorded at an air temperature of 22.5 °C were analysed, but due to poor recording quality, the lengths of calls and length of call intervals could not be measured for one of these series. Calls are a single, unpulsed “piping” notes produced in short series. Calls are extremely soft and were barely audible to the human ear. Call series contain 6-8 calls produced at a rate of 2.5-3.0 calls/s and last 2.0-2.9 s (mean 2.3 s) (Fig. 11a and b ). Call length is 133-162 ms (mean 143.4 ± 8.8 ms, n = 14) and length of call intervals is 168-376 ms (mean 250.6 ± 51.8 ms, n = 12). There are four harmonics with frequency peaks at 1.1, 2.2, 3.3 and 4.4 kHz; the third harmonic carries the dominant frequency (Fig. 11c ). Volume and pitch of calls both increase marginally during the course of call series.

Etymology.

The specific epithet Xenorhina thiekeorum is the Latinised patronymic adjective in genitive plural of the family name Thieke. It is given to recognise a very long-lasting friendship of the senior author with Heidi and Ulrich (Uli) Thieke from Berlin.

Comparisons with other species.

We compare Xenorhina thiekeorum sp. nov. with all congeners of a similar size (males with SUL ~ 18-25 mm) that have a single spike on each vomeropalatine.

Xenorhina anorbis has hind legs shorter (TL/SVL < 0.38 vs. > 0.38), digital discs on toes absent (vs. expanded discs present on toes 2-5) and END/IND ratio lower (1.26-1.32 vs. 1.36-1.54).

Xenorhina brachyrhyncha has legs longer (TL/SVL 0.46-0.49 vs. 0.40-0.44), head longer (HL/SVL 0.30-0.32 vs. 0.26-0.28) and broader (HW/SVL 0.35-0.38 vs. 0.32-0.33) and END/IND ratio much lower (1.06-1.13 vs. 1.36-1.54).

Xenorhina lanthanites has legs longer (TL/SUL 0.44-0.46 vs. 0.40-0.44), dilated disc only on 4th toe (vs. dilated discs on toes 2-5), T4D/F3D ratio higher (1.50-2.0 vs. 1.17-1.40), END/IND ratio lower (0.94-1.20 vs. 1.36-1.54) and advertisement call series much longer (up to more than one minute vs. a few seconds), with call intervals longer (397-896 ms vs. 168-376 ms) and repetition rate lower (1.2-1.8 vs. 2.5-3.0 calls/s).

Xenorhina mehelyi is probably much larger (SVL to > 35 mm vs. males 20.7-23.5 mm), internarial distance greater (IND/SVL 0.061-0.077 vs. 0.055-0.062) and has different advertisement calls: call series of X. mehelyi contain > 10 calls produced at a rate of 0.60 calls/s (vs. < 10 calls produced at a rate of 2.75 calls/s in Xenorhina thiekeorum sp. nov.); and dominant frequency is 0.88 kHz in X. mehelyi (vs. 3.3 kHz in X. thiekeorum ).

Xenorhina perexigua is smaller (16.7 mm vs. 20.7-23.5 mm SUL) and many body ratios differ from Xenorhina thiekeorum sp. nov. (Tables 2 and 4 ), but small sample sizes preclude robust comparisons of body ratios. Advertisement calls differ as follows: Xenorhina perexigua sp. nov. utters calls in series lasting more than 4 s, containing about 30 calls produced at rate of 6.8-6.9 calls/s (vs. call series lasting 2-3 s containing just 6-8 calls produced at rate of 2.5-3.0 calls/s); call length of Xenorhina perexigua sp. nov. is also much shorter (29-42 ms vs. 133-162 ms in Xenorhina thiekeorum sp. nov.).

Xenorhina pohleorum has fingers shorter (F3L/SUL 0.178-0.179 vs. 0.187-0.212), disc on third finger smaller (F3D/SUL 0.019-0.020 vs. 0.022-0.027), T4D/F3D ratio higher (1.75 vs. 1.17-1.40), END/IND ratio lower (1.31-1.33 vs. 1.36-1.54), eyes smaller (ED/SUL 0.057-0.064 vs. 0.068-0.078) and TyD/ED ratio higher (0.75-0.92 vs. 0.63-0.69). Moreover, call length of Xenorhina pohleorum sp. nov. is much shorter (~ 70-90 ms vs. 130-150 ms).

Xenorhina schiefenhoeveli is larger (SVL 26.7-30.7 mm vs. 20.7-23.5 mm), with ratio of END/IND lower (1.04-1.33 vs. 1.36-1.54) and different calls; call series last > 100 s (vs. 2-3 s in Xenorhina thiekeorum sp. nov.), with call intervals > 700 ms (vs. less than 400 ms).

Xenorhina tumulus is larger (SVL > 26.0 mm vs. < 24.0 mm), with internarial distance relatively longer (IND/SVL 0.063-0.069 vs. 0.055-0.062), distance between eye and naris relatively shorter (END/SVL 0.073-0.081 vs. 0.082-0.085), END/IND ratio lower (1.11-1.28 vs. 1.36-1.54) and call length shorter (60-70 ms vs. 133-162 ms).

Figures

Figure 10. Holotype (SAMA R 71651) of Xenorhina thiekeorum sp. nov. (a) Dorsolateral view in life; (b) Ventral view, (c) Volar view of right hand and (d) Thenar view of right foot of preserved specimen.

Figure 11. (a) Oscillogram; (b) Spectrogram and (c) amplitude spectrum of a series of six calls from the holotype of Xenorhina thiekeorum sp. nov.

Figure 16. Map of Papua New Guinea showing the known distributions of X. thiekeorum sp. nov. (blue circle), X. wiegankorum sp. nov. (yellow triangles) and X. woxvoldi sp. nov. (red square). Arrows indicate the type localities.